Corporate naming rights, whether it's a stadium or an office tower, boil down to ego, marketing and money, and now a London-based insurance brokerage with practically zero name recognition with the public gets its name attached to the tallest building in the Western Hemisphere.

What's far less certain is whether loyal Chicagoans, as well as tourists, will allow the "Willis Tower" name to stick.

The immediate reaction was obvious outside the Wacker Drive skyscraper Thursday, shortly after Willis announced it secured naming rights to the tower as part of its deal to relocate area offices to three floors there. Cell phone and digital cameras clicked away as word of the pending name change spread and people came to capture images of the Sears Tower name before it disappears in late July.

Many people, including hundreds chiming in online, appeared dead-set against embracing Sears Tower as anything different, despite the fact that the retailer it was named for left for the suburbs 17 years ago.

Joseph Plumeri, Willis Group's chairman and CEO, was incredulous at the negative reaction to his company's decision to relocate 500 employees to the tower in the midst of a recession.

"Would you rather have an iconic building with nobody in it, which doesn't say a lot about Chicago, or someone with enough faith to take the space?" he asked. "The headline should be: A company has decided to invest money in Chicago, and if you miss that headline, you've missed the side of the building by a mile and a half."

But in Chicago, say consumers and branding experts, it's just not that simple, because the city's attachment to the building is far more complex than recognizing its economic contribution. This is a city with a deep appreciation of tradition and a healthy ego, where some Chicagoans still mourn the switch from Marshall Field's to Macy's.

"It's our strong Midwestern values," said D. Joel Whalen, an assistant professor of marketing at DePaul University. "We know one of the hallmarks of quality is constancy, and change is not always good. We're friendly to everyone but we don't make friends quickly. It takes years to make a friend. You're from out of town and we don't know who you are."

When it was completed in 1973, the then-tallest building in the world became home to the then-largest retailer in the world, Sears, Roebuck and Co. Sears relocated to Hoffman Estates in 1992 but the name stayed behind.

The Skidmore, Owings & Merrill-designed building drew unwanted attention in the wake of the Sept. 11, 2001, attacks, amid worries that it could become a terrorist target. Some tenants left; others complained about tightened security procedures.

Currently, 85 percent of the building is leased, and commercial real estate experts say a name change may help leasing efforts going forward, particularly as the tower tries to woo more international firms like Willis.

For the building's existing tenants, the name change will cause them to re-evaluate how they refer to their workplaces and, more importantly, how they direct visitors to their offices.

"I still refer to [ Aon Center] as the Standard Oil building and I go to watch the White Sox at Comiskey Park," said Ronald Safer, managing partner at Sears Tower tenant Schiff Hardin LLP. He figures he'll tell clients his office can be found in "the structure formerly known as Sears Tower."

William Lozito, president of Strategic Name Development Inc., a Minneapolis-based consultancy, said Willis has an uphill battle on its hands, particularly because the Sears name is not being replaced with another familiar consumer brand. "I can predict for years people are going to call it Sears Tower because it's being replaced with an unknown."

Willis, which now will have a taller building to call its own than its cross-town competitor Aon Corp., will lease 140,000 square feet of the 110-story skyscraper. Plumeri said he asked for, and received, the naming rights for free, a comment immediately disputed by U.S. Equities Realty, the tower's leasing and property management firm.

"We are extremely pleased with the economics of this deal," said senior vice president Mike Kazmierczak, adding there was "significant financial consideration" for the naming rights.

Mayor Richard Daley shrugged his shoulders Thursday when reporters asked his thoughts on the name change. In the past, he has supported the renaming of such icons as Marshall Field's, and this seemed no different. "Sears moved out a long time ago," he said.